An outdoor coating composition having good weather resistance has conventionally been applied onto outdoor substrates such as building structures, displays, guard fences, instruments, machines and the like for the purpose of decoration or protection.
The outdoor coating composition used at present may include, for example, polyurethane resin based coating composition, fluorocarbon resin based coating composition and the like, but use of these coating compositions results in such disadvantages that a surface of a coated product may easily be stained and show poor appearance by influence due to dust, iron powder, rain, particularly acid rain, sunlight, etc. during outdoor exposure.
Besides the above coating compositions, a silicone resin based coating composition containing an alkoxysilane group-containing polymer as a resin component has been used as a highly weather-resistant coating composition. When a period of outdoor exposure is as long as six months or so, stain on the surface of a film formed from the above coating composition may be reduced, but the use of the above coating composition shows such a problem that the surface of the film formed therefrom may easily be stained when the period of outdoor exposure is shorter than six months.
As an example of a method of preventing stain on the film surface, Japanese Patent Application Laid-Open No. 221282/86 discloses a process which comprises coating an alkylsilicate solution in an organic solvent onto the surface of a molded product and a process which comprises incorporating alkylsilicate into a molded product of a thermoplastic resin. However, the above methods had such drawbacks that the film provided by the above methods shows poor properties in retension of stain resistance and durability.
The present inventors made intensive studies for the purpose of solving the above problems to find out that a coating composition obtained by incorporating an organosilicate and a condensate thereof into an organic coating composition provides a film hardly stained or showing good stain resistance, resulting in accomplishing the present invention.